CALYPSO grows primarily in the fall and early spring, blooming from late May to late June (Mousely 1924). The evergreen, solitary leaf, emerges in late August, overwinters, and shrivels soon after blooming. Capsules are set in June and July, and soon after there may be no visible signs of of this species. The new overwintering leaves usually begin to emerge in September (Caljouw 1981), but Vickery and Rooney (pers. observation) noted emerging leaves in mid August in Lee, Maine. Very few plants set fruit (Mosquin 1970). However, fairy slipper orchids produce thousands of seeds per capsule, which gives them the potential of good spread by seed.
Mousely (1924) reports that principal reproduction is by rhizomatous roots at the base of the tubers. Another factor contributing to the elusive qualities of this species is dormancy, one to several year periods being common (pers. obs.). Densities of this species vary from the usual one or two to the up to fifty plants per square foot reported by some references (Rooney, Gawler, Merry, Vickery pers. comm., Mosquin 1970). In Crystal Bog Preserve the population has fluctuated from one flowering plant in 1979 upwards to 12 blooming in spring of 1981; down to five flowers in spring of 1982. In fall of 1983 Mckellar & Rooney counted 40 sterile leaves and five plants with flower buds.
CALYPSO apparently is intolerant of soil temperatures in excess of 15 degrees C and of canopy cover less than 60% (Caljouw 1981). It is principally associated with Thuja occidentalis - growing in the shaded duff with little or no herbaceous competition.
In several sites in Maine, the cover has been extensively damaged by spruce budworm recently, allowing light to penetrate to the forest floor. The spring of 1983 marked the lowest population of CALYPSO at these sites since its discovery in 1979 (Rooney). The decline of flowering plants probably reflects the damage done to the cover by the budworm and perhaps frost damage to the tubers. The winter of '82/'83 was distinguished by the absence of the usual protective blanket of snow.
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